Nonconstant quality of auditory filters in the porpoises, Phocoena phocoena and Neophocaena phocaenoides (Cetacea, Phocoenidae)

Simultaneous tone-tone masking in conjunction with the envelope-following response (EFR) recording was used to obtain tuning curves in porpoises Phocoena phocoena and Neophocaena phocaenoides asiaeorientalis. The EFR was evoked by amplitude-modulated probes with a modulation rate of 1000 Hz and carrier frequencies from 22.5 to 140 kHz. Equivalent rectangular quality Q(ERB) of the obtained tuning curves varied from 8.3-8.6 at lower (22.5-32 kHz) probe frequencies to 44.8-47.4 at high (128-140 kHz) frequencies. The QERB dependence on probe frequency could be approximated by regression lines with a slope of 0.83 to 0.86 in log-log scale., which corresponded to almost frequency-proportional quality and almost constant bandwidth of 34 kHz. Thus, the frequency representation in the porpoise auditory system is much closer to a constant-bandwidth rather that to a constant-quality manner. (c) 2006 Acoustical Society of America.

元音和复合音识别中噪音分离机制的实验研究

Harmonicity is one of the important features of a vowel. It makes great contribution to pitch and quality of vowel. However, contribution of a mistuned harmonic will decrease as it is mistuned increasingly. A mistuned harmonic will be segregated as noise from complex by auditory system, which was called harmonic sieve (Duifhuis, 1982). According to Darwin (1986) and Moore et al (1985), the critical value of one mistuned harmonic would be segregated from vowel or complex is 3% to 8%－－Harmonic Mistuned Effect (HME). Further questions need to be answered. For example, how will the harmonic sieve separate noise or whether the critical value change when more than two harmonics are mistuned? And what affect the HME? Three experiments were conducted to these questions. Experiment one was dealt with the number of mistuned harmonics as a factor affecting the HME. The position effect of HME was concerned in experiment two. The last experiment considered the relationship between HME and phase of the mistuned harmonic. The results indicated that (1) the HME was much greater when more than two harmonics were mistuned than only one harmonic was mistuned; (2) harmonic position played an important role in HME, the higher the harmonic was, the less HME was found for the complex, and the closer to formant the harmonic stood, the more significant HME existed; and (3) phase did not affect the HME significantly, however, its indirect contribution still existed, which related to the starting amplitude of a mistuned harmonic.